Heat exchanger

ABSTRACT

A heat exchanger for exchanging heat between first and second duct portions of a ventilation system includes first and second heat pipe portions in the first and second duct portions, respectively. Each heat pipe portion can be a heat pipe subassembly including one or more vertical heat pipes fluidly coupled to top and bottom headers, which are respectively connected to the top and bottom headers of the other subassembly to form a refrigerant loop. One or more flow restrictors can block air flow through a respective section of the first or second duct portion. The blocked section can be operatively aligned with a segment of the respective heat pipe portion along which there is a low probability of refrigerant phase change. Each flow restrictor can be an adjustable damper. The damper(s) can be selectively opened and closed as the ventilation system switches between heating and cooling modes.

CROSS-REFERENCE TO RELATED APPLICATION DATA

This application is a division of U.S. patent application Ser. No.15/952,758, filed Apr. 13, 2018, titled HEAT EXCHANGER, the disclosureof which is incorporated herein in its entirety.

FIELD

This disclosure generally relates to a heat exchanger that provides heatrecovery in a climate control system.

BACKGROUND

Heat exchangers can be used in climate control systems to transfer heatbetween warm and cool air streams flowing through different ducts of thesystem. For example, a heat exchanger can be used to transfer heatbetween an exhaust air stream flowing through an exhaust air duct and asupply air stream (e.g., return air and/or outside air) flowing througha supply air duct. This concept is generally referred to as heatrecovery. The exhaust air stream and supply air stream will typically beat different temperatures. For example, when a climate control system isbeing used for heating a building, the exhaust air stream will berelatively warm and the supply air stream will be relatively cool. Inthis situation, a heat exchanger can be used to transfer heat from theexhaust air stream to the supply air stream to heat the supply airstream before it is fully heated by a heater. In this way, heat isrecovered from the warm exhaust air and used to warm the incoming supplyair. Conversely, when a ventilation system is used for cooling abuilding, the exhaust air stream will be relatively cool and the supplyair stream will be relatively warm. In this situation, the heatexchanger can be used to transfer heat from the supply air stream to theexhaust air stream to cool the supply air stream before it is furthercooled by an air conditioner. In this way, heat is moved from theincoming supply air stream to the exhaust air stream to pre-cool theincoming supply air stream. Some ventilation systems are used for bothheating and cooling a building over the course of a year.

SUMMARY

In one aspect, a heat exchanger for exchanging heat between first andsecond duct portions of a ventilation system comprises a heat pipesystem comprising a refrigerant. The heat pipe system includes a firstheat pipe portion and a second heat pipe portion that is configured tobe fluidly connected to the first heat pipe portion such that therefrigerant can flow through the heat pipe system between the first heatpipe portion and the second heat pipe portion. The first heat pipeportion is configured to be installed in the ventilation system insidethe first duct portion such that heat is transferrable between the firstheat pipe portion and air flowing through the first duct portion. Thesecond heat pipe portion is configured to be installed in theventilation system such that heat is transferrable between the secondheat pipe portion and air flowing through the second duct portion. Aflow restrictor is configured to be installed in the ventilation systeminside the first duct portion. The flow restrictor is configured tosubstantially restrict the air flowing through the first duct portionfrom flowing through a first section of the first duct portion and allowpassage of the air flowing through the first duct portion through asecond section of the first duct portion. Wherein the first heat pipeportion is received in both the first section of the first duct portionand the second section of the first duct portion.

In another aspect, a method of recovering heat in a ventilation systemhaving a supply duct and an exhaust duct comprises operating theventilation system in a cooling mode. While operating the ventilation inthe cooling mode, at least one step is performed from a group of coolingmode steps consisting of: arranging a top supply restrictor to restricta supply air stream in the supply duct from flowing through a topsection of the supply duct in which a top segment of a supply heat pipeportion of a heat exchanger is received; arranging a bottom exhaustrestrictor to restrict an exhaust air stream in the exhaust duct fromflowing through a bottom section of the exhaust duct in which a bottomsegment of an exhaust heat pipe portion of the heat exchanger isreceived; arranging a bottom supply restrictor to permit the supply airstream to flow through a bottom section of the supply duct in which abottom segment of the supply heat pipe portion is received; andarranging a top exhaust restrictor to permit the exhaust air stream toflow through a top section of the exhaust duct in which a top segment ofthe exhaust heat pipe portion is received. The ventilation system isoperated in a heating mode. While operating the ventilation system inheating mode, at least one step is performed from a group of heatingmode steps consisting of: arranging the top supply restrictor to permitthe supply air stream to flow through the top section of the supplyduct; arranging the bottom exhaust restrictor to permit the exhaust airstream to flow through the bottom section of the exhaust duct; arrangingthe bottom supply restrictor to restrict the supply air stream fromflowing through the bottom section of the supply duct; and arranging thetop exhaust restrictor to restrict the exhaust air stream from flowingthrough the top section of the exhaust duct.

In yet another aspect, a heat exchanger for exchanging heat in a duct ofa ventilation system comprises a heat pipe assembly configured to beinstalled in the ventilation system inside the duct such that heat istransferrable between the heat pipe assembly and air flowing through theduct. The heat pipe assembly includes a plurality of heat pipesextending vertically when the heat pipe assembly is installed in theduct. Each heat pipe has a height that is greater than about 36 inches(about 91 cm). A flow restrictor is configured to be installed in theventilation system inside the duct. The flow restrictor is configured tosubstantially restrict the air flowing through the duct from flowingthrough a first section of the duct and allow passage of the air flowingthrough the duct through a second section of the duct. The heat pipeassembly is received in both the first section of the duct and thesecond section of the duct

Other aspects will be in part apparent and in part pointed outhereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a heat exchanger installed in aventilation system;

FIG. 2 is a schematic illustration of a heat pipe system of the heatexchanger;

FIG. 3 is a schematic illustration of an evaporator portion of the heatexchanger installed in a first duct portion of the ventilation systemand includes a schematic representation of air flow through the firstduct portion;

FIG. 4 is a schematic illustration of a condenser portion of the heatexchanger installed in a second duct portion of the ventilation systemand includes a schematic representation of air flow through the secondduct portion;

FIG. 5 is a schematic illustration of another embodiment of a heatexchanger installed in the ventilation system; and

FIG. 6 is a schematic illustration of another embodiment of a heatexchanger installed in the ventilation system.

Corresponding reference characters indicate corresponding partsthroughout the drawings.

DETAILED DESCRIPTION

Referring to FIG. 1 , one embodiment of a heat exchanger is generallyindicated at reference number 10. The heat exchanger 10 is generallyconfigured to provide heat recovery in a ventilation system of a forcedair climate control system. For example, the illustrated heat exchanger10 is thought to be suitably configured for providing heat recovery in aventilation system that operates during the course of a year in both acooling mode and a heating mode (e.g., a two-season climate controlsystem). In the illustrated embodiment, the heat exchanger 10 isconfigured to provide heat recovery between a supply air duct SD(broadly, a first duct portion) and an exhaust air duct ED (broadly, asecond duct portion). In general, the ducts SD, ED are configured toreceive air streams SS, ES (FIGS. 3 and 4 ) of different temperatures(e.g., a warm air stream and a cool air stream). The heat exchanger 10could also be used to provide heat recovery between other duct portions,such as first and second portions of a single inline duct at which thetemperature of an air stream flowing through the duct is expected todiffer. In the illustrated embodiment, the ducts SD, ED are arrangedside-by-side such that the ducts are spaced apart along a horizontalaxis and disposed at a common height along a vertical axis. The ductscan have other arrangements in other embodiments.

Referring to FIG. 2 , the heat exchanger 10 includes a heat pipe system,generally indicated at 12. The illustrated heat pipe system 12 comprisesa supply heat pipe subassembly 14 (broadly, a first heat pipesubassembly) that is configured to be installed in the ventilationsystem in thermal communication with a supply air stream SS (FIG. 3 )flowing through the supply duct SD and an exhaust heat pipe subassembly16 (broadly, a second heat pipe subassembly) that is configured to beinstalled in the ventilation system in thermal communication with anexhaust air stream ES (FIG. 4 ) flowing through the exhaust duct ED. Inthe illustrated embodiment, each of the heat pipe subassemblies 14, 16includes a heat pipe portion that is configured to be installed insidethe respective duct SD, ED. Thus, the heat pipe portions of thesubassemblies 14, 16 are configured to be in direct thermal contact withthe air streams SS, ES as the air streams flow through the ducts SD, EDalong the respective heat pipe portions. A heat pipe portion could alsobe installed in a ventilation system in thermal communication with anair stream flowing through a duct portion in other ways withoutdeparting from the scope of the invention.

Each of the heat pipe subassemblies 14, 16 comprises a top header 20, abottom header 22, and a plurality of heat pipes 24 that extendvertically and provide fluid communication between the respective topheader and the respective bottom header. Other configurations are alsopossible without departing from the scope of the invention. Each of thetop and bottom headers 20, 22 can comprise a manifold having a mainpassage that is fluidly coupled to each of the heat pipes 24. In theillustrated embodiment, the top and bottom headers 20, 22 are locatedoutside of the respective duct SD, ED. In other embodiments, the headerscould be installed inside the duct with the vertical heat pipes.

The vertical heat pipes 24 individually and collectively comprise heatpipe portions received in the respective duct SD, ED. In one or moreembodiments, the vertical heat pipes 24 extend along an entirety of aheight of the respective duct SD, ED and are spaced apart along a widthof the respective duct. Two or more heat pipe subassemblies can also bevertically stacked inside a duct in some embodiments. In certainembodiments, the vertical heat pipes 24 have a height that is greaterthan about 36 inches (about 91 cm), such as greater than about 40 inches(about 102 cm), greater than about 45 inches (about 114 cm), greaterthan about 50 inches (about 127 cm), greater than about 55 inches (about140 cm), greater than about 60 inches (about 152.4 cm), greater thanabout 65 inches (about 165 cm), greater than about 70 inches (about 178cm), about 75 inches (about 191 cm), etc. The heat pipes can also haveother heights in one or more embodiments. Accordingly, the air streamsSS, ES can flow through the gaps between the heat pipes 24 as they flowthrough the respective ducts SD, ED. Referring to FIGS. 3 and 4 , only asingle row of vertical heat pipes 24 is shown in the illustratedembodiment. In other embodiments, however, a plurality of rows of heatpipes can be spaced apart in the direction of air flow through therespective duct. In certain embodiments, the vertical heat pipes in aplurality of rows of heat pipes can be offset from one another along thewidth of the duct. Additional rows of vertical heat pipes can be fluidlycoupled to the same headers 20, 22 or to different headers (e.g., therecan be a dedicated header for each row of heat pipes or for a set of twoor more rows of heat pipes). In one or more embodiments, heat transferfins (not shown) extend along the width of each duct SD, ED at spacedapart locations along the height of each duct such that the respectiveairstream SS, ES can flow through the gaps between the fins. Suitably,each fin can comprise a thin strip of thermally conductive material thatis thermally and physically connected to one or more vertical heat pipes24 in the respective duct SD, ED to transfer heat between the respectiveheat pipes and the respective air stream SS, ES.

The heat pipe system 12 is charged with a refrigerant that is suitablefor the temperature range of the ventilation system in which the heatexchanger 10 is installed. Referring again to FIGS. 1 and 2 , the supplyheat pipe subassembly 14 is fluidly connected to the exhaust heat pipesubassembly 16 such that the refrigerant can flow through the heat pipesystem 12 between the heat pipe subassemblies. More specifically, theillustrated heat pipe system 12 comprises a vapor conduit 30 thatprovides fluid communication between the top headers 20 of the heat pipesubassemblies 14, 16 and a liquid conduit 32 that provides fluidcommunication between the bottom headers 22 of the heat pipesubassemblies. The heat pipe system 12 thus defines a continuousrefrigerant flow loop extending from the top header 20 of the supplyheat pipe subassembly 14 in series through vapor conduit 30, the topheader of the exhaust heat pipe subassembly 16, the heat pipes 24 of theexhaust heat pipe subassembly, the bottom header 22 of the exhaust heatpipe subassembly, the liquid conduit 32, the bottom header of the supplyheat pipe subassembly, the heat pipes of the supply heat pipesubassembly, and back to the top header of the supply subassembly.Although the continuous refrigerant flow loop was described asproceeding in a clockwise direction through the passaging depicted inFIGS. 1 and 2 , it will be understood that the refrigerant can also flowin the opposite direction.

Referring to FIG. 2 , and as will be explained in further detail below,the heat pipe system 12 is configured so that either of the heat pipesubassemblies 14, 16 can function as an evaporator (e.g., an evaporatorheat pipe subassembly) that is configured to evaporate liquidrefrigerant while the other of the subassemblies functions as acondenser (e.g., a condenser heat pipe subassembly) that is configuredto condense refrigerant vapor. As will be appreciated by those skilledin the art, the heat pipe subassembly 12 is configured to transfer heatfrom the warmer of the air streams SS, ES to the cooler of the airstreams as the refrigerant in the heat pipe system 12 flows between theevaporator heat pipe subassembly 14, 16 and the condenser heat pipesubassembly. In general, heat from the warm air stream SS, ES isabsorbed by evaporation of the refrigerant in the evaporator heat pipesubassembly 14, 16, thereby cooling the warm air stream and warming therefrigerant. The warm, evaporated refrigerant flows through the topheader 20 of the evaporator heat pipe subassembly 14, 16 and through thevapor conduit 30 to the condenser heat pipe subassembly. In thecondenser heat pipe subassembly 14, 16, the cool air stream SS, ES flowsalong the heat pipes 24 and condenses the warm refrigerant vapor.Condensation of the refrigerant transfers heat to the cool air streamSS, ES, thereby warming the air stream and cooling the refrigerant. Thecool, condensed refrigerant flows along the liquid conduit 32 back tothe evaporator heat pipe subassembly. This heat recovery cycle can, incertain embodiments, continue passively in a closed loop.

Heat transfer between the air streams SS, ES and the heat exchanger 10is greatest at locations where refrigerant phase change is occurring.Evaporation in the evaporator heat pipe subassembly 14, 16 absorbs heatfrom the respective air stream SS, ES and condensation in the condenserheat pipe subassembly releases heat into the other air stream. Heatexchange between the heat pipe subassemblies 14, 16 and the air streamsSS, ES is maximized at locations along the heights of the heat pipes 24where evaporation or condensation is occurring. Heat exchange may besubstantially reduced where no evaporation or condensation is occurring.In the embodiment where heat pipe subassembly 14 is the evaporator heatpipe assembly and heat pipe subassembly 16 is the condenser heat pipeassembly, heat exchange is maximized generally at the bottom and middleportions of the evaporator heat pipe subassembly 14 and at the top andmiddle portions of the condenser heat pipe subassembly 16, as will beexplained in further detail below.

In the illustrated embodiment, the supply subassembly 14 and the exhaustsubassembly 16 are located at about the same height and the vaporconduit 30 and the liquid conduit 32 each extend generally horizontally.Accordingly, in the illustrated heat pipe system 12, refrigerant isconfigured to flow passively between the subassemblies 14, 16 and is notgravity driven. In other embodiments, the heat pipe system can bearranged so that refrigerant flow between the subassemblies isgravity-assisted (e.g., by orienting the liquid conduit to slope towardthe subassembly functioning as an evaporator). In addition, a pump canbe used to drive refrigerant flow through the heat pipe system incertain embodiments.

Regardless of the mode by which refrigerant is driven through a heatpipe loop, because of gravity, liquid refrigerant tends to flow towardthe bottom end of the heat pipe system 12 and vaporized refrigeranttends to flow toward the top end of the heat pipe system. As a result,refrigerant vapor may collect in the top segments of the heat pipes 24(as well as in the top headers 20 and the vapor conduit 30); andsimilarly, liquid may collect in the bottom segments of the heat pipes(as well as in the bottom headers 22 and the liquid conduit 32). In theevaporator heat pipe subassembly 14, 16, the refrigerant vapor thatcollects in the top segments of the heat pipes 24 can cause diminishedheat transfer at the top segments of the heat pipes in comparison withthe bottom and middle segments of the heat pipes where liquidrefrigerant that may be evaporated is present. Similarly, in thecondenser subassembly 14, 16, the liquid refrigerant that collects inthe bottom segments of the heat pipes 24 can cause diminished heattransfer at the bottom segments of the heat pipes in comparison with thetop and middle segments of the heat pipes where refrigerant vapor thatmay be condensed is present. As explained below, the illustrated heatexchanger 10 is generally configured to selectively restrict air flowthrough low heat-transfer sections of the ducts SD, ED that are alignedwith segments of the heat pipes 24 in which collected refrigerant vaporor liquid refrigerant may reduce heat transfer capacity. Restricting airflow in this manner is thought to maximize the amount of the air streamsSS, ES that flows along the segments of the heat pipes 24 where heattransfer potential may be greater because more evaporation orcondensation may be possible.

Referring to FIG. 1 , the illustrated heat exchanger 10 includes aplurality of adjustable dampers 40, 42, 50, 52 (broadly, adjustable flowrestrictors or, more generally, flow restrictors) that are configured tobe installed in the ducts SD, ED for selectively restricting therespective air streams SS, ES from flowing through respective sectionsof the ducts. Other types of adjustable flow restrictors (e.g., gatevalves) or static flow restrictors (e.g., one or more fixed plates, oran enclosure) could also be used in other embodiments. In theillustrated embodiment, the heat exchanger 10 comprises a top supplydamper 40 installed in the top section of the supply duct SD, a bottomsupply damper 42 installed in the bottom section of the supply duct, atop exhaust damper 50 installed in the top section of the exhaust ductED, and a bottom exhaust damper 52 installed in the bottom section ofthe exhaust duct. The middle sections of the ducts SD, ED aresubstantially free of any structure (besides the respective heat pipes24 and thermal fins) that restricts flow through the middle sections.Each heat pipe 24 includes a respective segment that is received in thetop section, the middle section, and the bottom section of therespective duct SD, ED, as delimited by the respective dampers 40, 42,50, 52. Other embodiments (some of which are described in reference toFIGS. 5 and 6 below), can comprise other arrangements of dampers withoutdeparting from the scope of the invention. For example, when multipleheat pipe subassemblies are stacked vertically in a single duct,adjustable dampers can be arranged in operative alignment with the topsegment and/or bottom segment of one or more the heat pipe subassembliesin the stack (e.g., a damper can be located at a middle section of theduct that is operatively aligned with a top segment of a bottom heatpipe subassembly or a bottom segment of a top heat pipe subassembly,etc.).

Each damper 40, 42, 50, 52 comprises a frame (e.g., a support)configured to mount the damper in the respective duct SD, ED inoperative alignment with a respective section of the respective duct SD,ED. Referring to FIGS. 3 and 4 , the frame of each of the top dampers40, 50 defines a top plenum 60 (broadly, a top section) of therespective duct SD, ED, and the frame of each of the bottom dampers 42,52 defines a bottom plenum 62 (broadly, a bottom section) of therespective duct that is spaced apart from the respective top plenum. Thetop and bottom dampers 40, 42, 50, 52 in each duct SD, ED define amiddle flow plenum 64 (broadly, a middle section) between the top andbottom plenums. In one embodiment, the frames of the dampers 40, 42, 50,42 define respective plenums 60, 62, 64 that extend from respectiveupstream ends spaced apart upstream of the heat pipes 24 of therespective heat pipe subassembly 14, 16 to respective downstream endsspaced apart downstream of the heat pipes of the respective heat pipesubassembly. As will be explained in further detail below, theadjustable dampers 40, 42, 50, 52 are configured to selectively restrictair flow through the plenums defined by their frames. In otherembodiments, the frames of the adjustable dampers could have otherconfigurations, e.g., the frames could define plenums that are locatedentirely upstream of the respective heat pipes.

In general, the adjustable dampers 40, 42, 50, 52 are selectivelyopenable to allow passage of the air streams SS, ES through therespective plenums and are selectively closable to restrict air flowthrough the respective plenums. Referring still to FIGS. 3 and 4 , inthe illustrated embodiment, each damper 40, 42, 50, 52 includes aplurality of damper plates that are selectively pivotable aboutrespective horizontal axes between an open configuration (e.g., thebottom supply damper 42 and the top exhaust damper 50) and a closedconfiguration (e.g., the top supply damper 40 and the bottom exhaustdamper 52). In one embodiment, the dampers 40, 42, 50, 52 are manuallyadjustable between the open and closed configurations; in anotherembodiment, the dampers include one or more actuators (not shown) thatare configured to drive movement of the damper plates to open and closethe dampers. For example, the heat exchanger 10 can include a controller(not shown) that is configured to automatically direct the actuators toopen and close the dampers based on which of the air streams SS, ES hasa greater temperature or the mode of operation (e.g., cooling mode,heating mode) of the ventilation system.

In the closed configuration of each damper 40, 42, 50, 52, the damperplates form a flow restrictor that is arranged to restrict air fromflowing through the respective plenum 60, 62. In one or moreembodiments, each of the flow restrictors provided by the closed dampers40, 42, 50, 52 extends along substantially an entirety of a width of therespective duct SD, ED and extends along only a partial segment that isless than an entirety of the height of the respective duct. For example,the flow restrictors may extend along about ⅓ of the height of therespective duct. In another embodiment, the flow restrictors may extendalong about ¼ of the height of the respective duct. When closed, eachdamper 40, 42, 50, 52 is configured to substantially restrict therespective air stream SS, ES from flowing along segments of the heatpipes 24 that are received in the respective plenum 60, 62. In contrast,when each damper 40, 42, 50, 52 is open, gaps are provided between thedamper plates, and the respective air stream SS, ES can flow through thegaps and through the respective plenum 60, 62. Thus, in the openconfiguration of each damper 40, 42, 50, 52, the respective airstreamSS, ES can flow along the segments of the heat pipes 24 that arereceived in the respective plenum 60, 62. In the illustrated embodiment,the damper plates of the dampers 40, 42, 50, 52 when the damper isclosed is located directly upstream from the segments of the heat pipes24 that are received in the respective plenum 60, 62. In otherembodiments, adjustable damper plates can also be included at a locationdownstream from the heat pipes. Still other adjustable and static flowrestrictor arrangements are also possible without departing from thescope of the invention.

In one embodiment, during use, the top damper 40, 50 is opened when therespective heat pipe subassembly 14, 16 is functioning as a condenser(e.g., when the respective air stream SS, ES comprises a cool airstream) and the top damper is closed when the respective heat pipesubassembly is functioning as an evaporator (e.g., when the respectiveair stream comprises a warm air stream). Conversely, the bottom damper42, 52 is closed when the respective heat pipe subassembly 14, 16 isfunctioning as a condenser (e.g., when the respective air stream SS, EScomprises a cool air stream) and the bottom damper is opened when therespective heat pipe subassembly is functioning as an evaporator (e.g.,when the respective air stream comprises a warm air stream).

When a heat pipe subassembly 14, 16 is functioning as a condenser, theair stream SS, ES flowing through the respective duct SD, ED comprises acool air stream. Opening the top damper 40, 50 when the respective heatpipe subassembly 14, 16 is functioning as a condenser allows therespective cool air stream to flow through the respective top plenum 60along the top segments of the that heat pipes 24, which contain warm,condensable refrigerant vapor. Heat is transferred from the warmrefrigerant vapor in the top segments and middle segments of the heatpipes 24 to the respective cool air stream SS, ES, thus condensing therefrigerant vapor. Closing the bottom damper 42, 52 when the respectiveheat pipe subassembly 14, 16 is functioning as a condenser restricts therespective air stream SS, ES from flowing through the bottom plenum 62across the bottom segments of the heat pipes 24, which contain collectedcondensed liquid refrigerant that is not capable of transferring heat tothe air stream by condensation. Thus, when the respective heat pipesubassembly 14, 16 is functioning as a condenser, opening the respectivetop damper 40, 50 and closing the respective bottom damper directssubstantially all of the cool air stream SS, ES flowing through therespective duct SD, ED to flow across the condenser heat pipesubassembly along the middle and upper segments of the heat pipes 24,where condensation of the refrigerant is most likely to occur, andsubstantially restricts the air stream from flowing along the bottomsegments of the heat pipes where condensation is less likely to occur.

When a heat pipe subassembly 14, 16 is functioning as an evaporator, theair stream SS, ES flowing through the respective duct SD, ED comprises awarm air stream. Closing the respective top damper 40, 50 when the heatpipe subassembly 14, 16 is functioning as an evaporator restricts therespective air stream SS, ES from flowing through the top plenum 60along the top segments of the heat pipes 24, which contain collectedrefrigerant vapor that is not capable of absorbing heat from the airstream by evaporation. In contrast, opening the bottom damper 42, 52allows the respective warm air stream SS, ES to flow through therespective bottom plenum 62 across the bottom segments of the that heatpipes 24, which contain cool, liquid refrigerant that can absorb heat byevaporation. Heat is thus transferred from the warm air stream ES, SS tothe bottom segments and middle segments of the heat pipes 24, therebyevaporating the liquid refrigerant in the bottom and middle segments.Thus, when the respective heat pipe subassembly 14, 16 is functioning asan evaporator, opening the respective bottom damper 42, 52 and closingthe respective top damper 40, 50 directs substantially all of the warmair stream SS, ES flowing through the respective duct SD, ED to flowacross the heat pipe subassembly along the middle and bottom segments ofthe heat pipes 24, where evaporation of the refrigerant is most likelyto occur, and substantially restricts the warm air stream from flowingalong the top segments of the heat pipes where evaporation is lesslikely to occur.

A method of using the heat exchanger 10 in a two-season ventilationsystem will now be described. In a two-season ventilation system, whenthe ventilation system switches to a cooling mode, the supply heat pipesubassembly 14 functions as an evaporator and the exhaust heat pipesubassembly 16 functions as a condenser. Thus, when the two-seasonventilation system switches to a cooling mode, the top damper 40 in thesupply duct SD is closed and the bottom damper 42 in the supply duct isopened (as shown in FIG. 3 ) and the top damper 50 of the exhaust ductED is opened and the bottom damper 52 of the exhaust duct is closed (asshown in FIG. 4 ). When the ventilation system switches to a heatingmode, the supply heat pipe subassembly 14 functions as a condenser andthe exhaust heat pipe subassembly 16 functions as an evaporator. Thus,the top damper 40 in the supply duct SD is opened and the bottom damper42 in the supply duct is closed and the top damper 50 in the exhaustduct ED is closed and the bottom damper 52 in the exhaust duct is openedas shown in FIG. 4 .

In a ventilation system that operates full-time in the heating mode,static flow restrictors could be used in the position(s) of one or moreof the closed dampers in the heating mode of the two-season ventilationsystem described above. Likewise, in a ventilation system that operatesfull-time in the cooling mode, static flow restrictors could be used inthe position(s) of one or more of the closed dampers in the cooling modeof the two-season ventilation system described above.

Referring to FIG. 5 , another embodiment of a heat exchanger isgenerally indicated at reference number 10′. The heat exchanger 10′ issubstantially identical to the heat exchanger 10, and correspondingparts are given corresponding reference numbers, plus a prime symbol. Incomparison with the heat exchanger 10, the heat exchanger 10′ includes asubstantially identical heat pipe system 12′ comprising heat pipeassemblies 14′, 16′ that are configured to be installed in the supplyduct SD and the exhaust duct ED such that vertical heat pipes 24′ ofeach subassembly are received inside the respective duct. In addition,the heat exchanger 10′ comprises bottom adjustable dampers 42′, 52′ thatare substantially identical to the bottom adjustable dampers 42, 52described above. Unlike the heat exchanger 10, however, the heatexchanger 10′ does not include top adjustable dampers. Thus, the heatexchanger 10′ is a simplified system with fewer components than the heatexchanger 10. In a two-season ventilation system, the bottom adjustabledampers 42′, 52′ can be used in the same manner as described above forthe bottom adjustable dampers 42, 52 of the heat exchanger 10.

Referring to FIG. 6 , another embodiment of a heat exchanger isgenerally indicated at reference number 10″. The heat exchanger 10″ issubstantially identical to the heat exchanger 10, and correspondingparts are given corresponding reference numbers, plus a double-primesymbol. In comparison with the heat exchanger 10, the heat exchanger 10″includes a substantially identical heat pipe system 12″ comprising heatpipe assemblies 14″, 16″ that are configured to be installed in thesupply duct SD and the exhaust duct ED such that vertical heat pipes 24″of each subassembly are received inside the respective duct. Inaddition, the heat exchanger 10″ comprises top and bottom adjustabledampers 40″, 42″ that are operatively aligned with the first heat pipesubassembly 14″. The top and bottom dampers 40″, 42″ can have any of thefeatures of the dampers 40, 42 described above. Unlike the heatexchanger 10, the heat exchanger 10″ does not include adjustable dampersthat are operatively aligned with the second heat pipe subassembly 16″.Thus, the heat exchanger 10″ is a simplified system with fewercomponents than the heat exchanger 10. In the illustrated embodiment,the dampers 40″, 42″ are located in only the supply duct SD and not theexhaust duct ED. In a two-season ventilation system, the adjustabledampers 40″, 42″ can be used in the same manner as described above forthe adjustable dampers 40, 42 of the heat exchanger 10. In one or moreembodiments, the top and bottom dampers can be included in only theexhaust duct; and in these embodiments, the dampers could be used in thesame manner as described of the adjustable dampers 50, 52 in atwo-season ventilation system. In further embodiments, it iscontemplated that the heat exchanger can have only a single adjustabledamper (e.g., a single adjustable damper that is operatively alignedwith the top segment or the bottom segment of a heat pipe subassembly ina supply duct, in an exhaust duct, or in another duct portion). In atwo-season ventilation system, a single damper can be used in the samemanner as described above for the adjustable damper 40, 42, 50, 52 atthe corresponding position in the heat exchanger 10.

When introducing elements of the present invention or the preferredembodiments(s) thereof, the articles “a”, “an”, “the” and “said” areintended to mean that there are one or more of the elements. The terms“comprising”, “including” and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above products and methodswithout departing from the scope of the invention, it is intended thatall matter contained in the above description shall be interpreted asillustrative and not in a limiting sense.

What is claimed is:
 1. A method of recovering heat in a ventilationsystem having a supply duct and an exhaust duct, the ventilation systemoperating in a heating mode, the method comprising: permitting a supplyair stream in the supply duct to flow through a top section of thesupply duct in which a top segment of a supply heat pipe portion isreceived; restricting the supply air stream in the supply duct fromflowing through a bottom section of the supply duct in which a bottomsegment of a supply heat pipe portion is received; and restricting theexhaust air stream in the exhaust duct from flowing through a topsection of the exhaust duct in which a top segment of an exhaust supplyheat pipe portion is received.
 2. A method of recovering heat in aventilation system having a supply duct and an exhaust duct, theventilation system operating in a heating mode, the method comprising:permitting a supply air stream in the supply duct to flow through a topsection of the supply duct in which a top segment of a supply heat pipeportion is received; restricting the supply air stream in the supplyduct from flowing through a bottom section of the supply duct in which abottom segment of a supply heat pipe portion is received; permitting anexhaust air stream in the exhaust duct to flow through a bottom sectionof the exhaust duct in which a bottom segment of an exhaust supply heatpipe portion is received; and restricting the exhaust air stream in theexhaust duct from flowing through a top section of the exhaust duct inwhich a top segment of an exhaust supply heat pipe portion is received.3. A method of recovering heat in a ventilation system having a supplyduct and an exhaust duct, the ventilation system operating in a heatingmode, the method comprising: permitting an exhaust air stream in theexhaust duct to flow through a bottom section of the exhaust duct inwhich a bottom segment of an exhaust heat pipe portion is received;restricting the exhaust air stream in the exhaust duct from flowingthrough a top section of the exhaust duct in which a top segment of anexhaust heat pipe portion is received; and restricting a supply airstream in the supply duct from flowing through a bottom section of thesupply duct in which a bottom segment of a supply heat pipe portion isreceived.
 4. A method of recovering heat in a ventilation system havinga supply duct and an exhaust duct, the ventilation system operating in aheating mode, the method comprising: permitting an exhaust air stream inthe exhaust duct to flow through a bottom section of the exhaust duct inwhich a bottom segment of an exhaust heat pipe portion is received; andrestricting the exhaust air stream in the exhaust duct from flowingthrough a top section of the exhaust duct in which a top segment of anexhaust heat pipe portion is received; permitting a supply air stream inthe supply duct to flow through a top section of the supply duct inwhich a top segment of a supply heat pipe portion is received; andrestricting the supply air stream in the supply duct from flowingthrough a bottom section of the supply duct in which a bottom segment ofa supply heat pipe portion is received.